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Engines using the Diesel cycle are usually more efficient, although the Diesel cycle itself is less efficient at equal compression ratios. Since diesel engines use much higher compression ratios (the heat of compression is used to ignite the slow-burning diesel fuel), that higher ratio more than compensates for air pumping losses within the engine.
In petrol (gasoline) engines used in passenger cars for the past 20 years, compression ratios have typically been between 8:1 and 12:1. Several production engines have used higher compression ratios, including: Cars built from 1955 to 1972 which were designed for high-octane leaded gasoline, which allowed compression ratios up to 13:1.
A diesel cycle engine can be as much as 40% to 50% efficient at converting fuel into work, [2] where a typical automotive gasoline engine's efficiency is about 25% to 30%. [3] [4] In general, an engine is designed to run on a single fuel source and substituting one fuel for another may affect the thermal efficiency.
The EPA rated the Nissan Leaf electric car with a combined fuel economy of 99 MPGe, [9] and rated the Chevrolet Volt plug-in hybrid with a combined fuel economy of 93 MPGe in all-electric mode, 37 MPG when operating with gasoline only, and an overall fuel economy rating of 60 mpg-US (3.9 L/100 km) combining power from electricity and gasoline.
1952 Shell Oil film showing the development of the diesel engine from 1877. The diesel engine, named after the German engineer Rudolf Diesel, is an internal combustion engine in which ignition of diesel fuel is caused by the elevated temperature of the air in the cylinder due to mechanical compression; thus, the diesel engine is called a compression-ignition engine (CI engine).
Fuel efficiency (or fuel economy) is a form of thermal efficiency, meaning the ratio of effort to result of a process that converts chemical potential energy contained in a carrier into kinetic energy or work.
A typical turbocharged V8 diesel engine might have an engine power of 250 kW (340 hp) and a mass of 380 kg (840 lb), [1] giving it a power-to-weight ratio of 0.65 kW/kg (0.40 hp/lb). Examples of high power-to-weight ratios can often be found in turbines.
The following table takes values as an example for the specific fuel consumption of several types of engines. For specific engines values can and often do differ from the table values shown below. Energy efficiency is based on a lower heating value of 42.7 MJ/kg (84.3 g/(kW⋅h)) for diesel fuel and jet fuel, 43.9 MJ/kg (82 g/(kW⋅h)) for ...